1. Field of the Invention
The present invention relates to a charged particle beam apparatus and a charged particle beam resolution measuring method. More particularly but not exclusively, this invention relates to an electron beam resolution measurement method adaptable for use in a charged particle beam apparatus for irradiating an electron beam onto a workpiece while variably shaping the electron beam. This invention also relates to an apparatus for implementation of such method.
2. Related Art
Lithography technology with contribution to semiconductor device miniaturization is a very important process among semiconductor manufacturing processes because it offers a unique feature of pattern generation capability. In recent years, with an increase in integration density of LSI chips, circuit line widths required for semiconductor devices are becoming more smaller year by year. To form a desired circuit pattern on these semiconductor devices, a need is felt to use a high-accuracy original pattern (also known as a reticle or a mask). Note here that electron ray (electron beam) pattern writing techniques are inherently superior in image resolution and, for this reason, are widely employed in the manufacture of such high-accuracy original pattern.
FIG. 11 is a conceptual diagram for explanation of an operation of one prior known variable-shaped electron beam (EB) pattern writing apparatus.
The variable-shaped EB writing apparatus operates in a way which follows. A first aperture 410 has a rectangular opening or hole 411, which formed therein for shaping an electron beam 330. A second aperture 420 has therein a variable shaping rectangular hole 421 for reshaping the electron beam 330 that passed through the hole 411 into a desired rectangular shape. The electron beam 330, which was emitted from a charged particle source 430 and has passed through the hole 411, is deflected by a deflector. Then, it passes through part of the variable shaping hole 421 and is then irradiated onto a workpiece 340, which is mounted on a stage. This stage is driven to move continuously in a specified one direction (e.g., X direction) during pattern writing. More specifically, a rectangular beam shape capable of penetrating both the hole 411 and the variable shaping hole 421 is shot to a pattern write area of the workpiece 340 which is placed on the stage that moves continuously. This technique for forming desired shapes while letting the beam penetrate both the hole 411 and variable shaping hole 421 is called the variable shaping scheme.
The accuracy and minimum image resolution size of a pattern that was formed using the above-stated EB lithographic apparatus are in close relationship with the resolving power of a beam used. On the other hand, in the case of a pattern being written on a substrate, there must exist several factors for materially degrading the resolution (i.e., process resolution), which factors are caused by the contrast of a resist film coated on the substrate and/or some processes, such as oxidation diffusion of a resist of the chemical amplification type. In currently available EB lithographic tools, the beam resolution of an EB tool per se has been improved (lessened), whereby it has been made equal to or smaller in value than the process resolution in a computational sense.
Here, a beam intensity distribution of the electron beam 330 to be irradiated onto the workpiece 340 is such that the electron beam 330 is scanned in such a way that the electron beam 330 is irradiated on a metallic mark having its size which is sufficiently less than the beam size of electron ray 330. And, a technique for performing instrumentation of reflected electrons from the metal mark is known (for example, see JP-A-4-242919). And, from the beam intensity distribution of the electron ray 330 thus obtained, it is possible to obtain the beam resolution of electron ray 300.
However, the beam intensity distribution obtained in this way is largely deviated from the waveform of an error function.
FIG. 12 is a diagram showing one example of the beam intensity distribution.
In FIG. 12, the beam intensity distribution indicates a result of measurement for instrumentation of reflected electrons from the metal mark by the scanning of an electron beam on the metal mark. Here, the beam intensity distribution is ideally defined by an error function F(x). However, the beam intensity distribution obtained (measured value) has been appreciably deviated from the waveform of such error function. One reason of this is that a distribution due to scattering from the metal mark used for the measurement is combined or “synthesized” together. Another reason considered is that the shape of such metal mark affects it. Accordingly, there is a problem as to unwanted increases in value of a beam resolution obtained when compared with the inherent beam resolution. This would result in peak out of the measurement result, which in turn leads to occurrence of a limit in measurable range also. Thus, it has been unable to measure small resolution.